The present invention relates to the field of semiconductor packaging, and more specifically to a boat for holding and aligning semiconductor flip chip packages during assembly.
Conventional flip chip package assemblies derive their name from the fact that an interconnect die, having all terminations (e.g., solder pads or bump contacts) on one surface, is flipped over for attachment to a substrate in a manner that allows the interconnect die terminations to couple with the substrate to form an electrical and mechanical connection. Flip chip assemblies and flip chip packages are supported because the interconnect die and other components consume limited substrate space, thereby enabling the formation of flip chip packages having high density and low inductance.
In a conventional flip chip assembly process, the die and substrate pass through flux dipping and chip mounter machines, wherein a bonding material, such as solder, is applied to the die and substrate and then the parts are mounted together. The die/substrate combination is then passed through a reflow oven that heats the bonding material to a temperature adequate to melt the material and attach the die to the substrate. The semi-assembled flip chip package can then be transported to a flux cleaning machine, an underfill dispenser and a vertical cure oven. Manufacturers can alter this process by adding or removing steps. The elements of each step may also vary depending on the particular semiconductor package being assembled and a manufacturer""s specific requirements.
In an effort to improve yield percentages and increase production speeds, many of the machines involved in flip chip assembly are typically programmed to perform the same function repeatedly and according to standardized parameters. Standardized package location is one such parameter. Flip chip assembly machines are programmed to assume that a package is in a precise location when the package enters a particular assembly step, such as die mounting, fluxing or seal placement. This allows the machine to go to the same location every time in order to complete its assigned task in the assembly process. In order for this kind of standardized repetition to yield positive production benefits, the package must be precisely positioned at an expected location, otherwise inefficiency results. For example, the machine will still complete its task without regard to package location resulting in an improperly assembled package that must either be reworked or discarded. In other instances, the machine may be programmed to look for the package before performing its assigned task, thereby reducing the need for rework, but also disadvantageously slowing production. Consequently, semiconductor device production is improved when the components are held in a precise location throughout the assembly process in way that allows each machine to perform its task as programmed.
Unassembled and semi-assembled flip chip packages are usually held in a carrying device during flip chip assembly. Carrying devices are useful because they make it easier for manufacturers to transport packages without direct physical contact, thereby reducing the likelihood of contamination and other damage attendant upon excessive handling. Carrying devices also make it easier to increase production speeds, because their ability to hold multiple flip chip packages allows manufacturers to move several packages at once and allows machines to work on more than one semiconductor package at a time or to move quickly from one package to another. However, a manufacturer""s ability to enjoy these benefits depends on whether package placement can be maintained in a standardized location during flip chip assembly. However, such package retention is difficult for at least two reasons.
First, semiconductor packages come in varying dimensions, thereby imposing a limitation on the extent to which manufacturers can rely on a carrying device maintaining a package in a precise location. For example, some packages are too large to fit into a standardized carrying device holding pocket, while others are so small that they fall through the hole in the bottom of the pocket. Package weight also affects package retention in a carrying device holding pocket. For example, lighter packages are easily jostled out of the pocket during transport or assembly. If a flip chip package does not fit or remain in the carrying device holding pocket, a machine will not operate properly according to package location-dependent instructions.
Existing carrying device designs exacerbate this problem. Currently, the same carrying device holds flip chip packages of all sizes, supported on a single shelf. The pocket opening, shelf size and hole though the pocket bottom are not designed to accommodate specific package sizes. Thus, if the package is smaller in length or width than the pocket opening, the package can slide around on the shelf in varying directions (e.g., side to side, up and down, or pivoting from a package corner). The resulting friction or collision between the carrying device and the flip chip package can damage the substrate, die or any other attached flip chip package elements (e.g., pins or balls). Furthermore, this movement moves the flip chip package from its precise location within the carrying device holding pocket, therefore increasing the likelihood that a flip chip assembly machine will be unable to properly perform its assigned task.
There is a need for a carrying device that can retain flip chip packages (e.g., ceramic or organic flip chip packages) in place during flip chip assembly.
The present invention comprises a boat for maintaining flip chip packages in place during assembly. Embodiments of the present invention include a boat for holding flip chip packages (e.g., ceramic or organic flip chip packages) having a bottom layer with an array of four-sided through-holes and a top layer having an array of through-holes with tabs extending from the sides of the through-hole. Each through-hole in the bottom layer is smaller than the overlying top layer through-hole. The top layer is attached to the bottom layer so that the central axis of each bottom layer through-hole is substantially aligned with the central axis of an overlying top layer through-hole. An alignment mechanism ensures that lids are accurately placed on flip chip packages held in the boat during assembly.
Boats in accordance with embodiments of the present invention advantageously maintain organic and ceramic flip chip packages in place in a standardized location in the boat during assembly, thereby improving production standardization and enabling assembly steps to be completed rapidly and repeatedly with little or no human intervention. In addition, damage that can occur when an assembly step is attempted or completed on a ceramic or organic flip chip package improperly seated in the boat is avoided or significantly limited.
In accordance with embodiments of the present invention, packages are prevented from extending through or falling out of the boat, thereby increasing manufacturing through put and reducing costs vis-xc3xa1-vis conventional carrying devices. In addition, boats can be designed to accommodate flip chip packages of varying sizes, thereby enabling manufacturers to use the same boat for many different flip chip packages, eliminating the need for multiple boats and for retrofitting assembly equipment to accommodate different flip chip boat designs.
Other advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description. The embodiments shown and described provide illustration of the best mode contemplated for carrying out the invention. The invention is capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive.